1. Field of the Invention
The present invention relates to an image forming apparatus with a paper feed port unable to detect paper size in advance, such as a paper feed port to which a multiple manual paper feed tray or a universal cassette is attached.
The present invention also relates to an image forming apparatus and, more particularly, to an image forming apparatus suitable for an electrophotographic printer with a manual paper feed mechanism having no means for determining paper size.
2. Related Background Art
A conventional electrophotographic printer of this type has a mechanism as shown in FIG. 1. Referring to FIG. 1, this electrophotographic printer comprises a photoconductive drum 1 as an electrostatic latent image carrier, a semiconductor laser 2 as a light source, and a rotary polygon mirror 3. A laser beam 4 scans the surface of the photoconductive drum 1 via the rotary polygon mirror 3.
The printer also comprises a charging roller 5 for uniformly charging the photoconductive drum 1, a developing device 6 for developing an electrostatic latent image formed on the photoconductive drum 1 by using toner, a transfer roller 7 for transferring the developed toner image onto a predetermined sheet of paper, and a fixing roller 8 for fixing the toner image transferred to the paper by fusing.
A cassette paper feed roller 9 feeds paper from a cassette capable of identifying a paper size into a conveyance path, and a manual paper feed roller 10 feeds paper from a manual paper feed port incapable of identifying a paper size into the conveyance path.
Registration rollers 11 abut against the leading end of fed paper to correct a ramp of the paper and synchronize the timing at which an image is written on the photoconductive drum 1 with the timing at which paper is conveyed to it. A registration sensor 12 senses the leading end of paper and measures the length of manually fed paper in the direction of conveyance. The printer further comprises paper delivery rollers 13 for delivering paper subjected to fixing and a paper delivery sensor 14 for detecting the presence/absence of fixed paper.
FIG. 2 shows the circuit configuration of a control system for controlling the mechanism as described above.
Referring to FIG. 2, a printer controller 100 develops input image code data from external equipment, such as a host computer, into bit data required for printing of the printer and reads internal information of the printer through, e.g., transmission and displays the information.
An engine control section 101 controls the operations of individual parts of a printer engine in accordance with designations from the printer controller 100 and identifies for the printer controller 100 the printer internal information.
A paper conveyance control section 102 controls driving and stopping of, e.g., motors and rollers for paper conveyance in accordance with designations from the engine control section 101.
A high-voltage (high pressure) control section 103 controls high-voltage outputs of charging, developing, and transfer steps in accordance with designations from the engine control section 101.
An optical system control section 104 controls driving/stopping of a scanner motor and ON/OFF of a laser on the basis of designations from the engine control section 101.
A sensor input section 105 transmits information from the registration sensor and the paper delivery sensor to the engine control section 101.
A fixing device temperature control section 106 controls the temperature of a fixing device to a temperature designated by the engine control section 101.
FIG. 3, which comprises FIGS. 3A and 3B, shows a control sequence performed by the engine control section 101 to designate manual paper feed in the above control system. This flow chart illustrates a control sequence from manual feed of paper upon reception of a print request signal from the printer controller 100 to a comparison between a designated paper size and the size of the paper being actually conveyed.
First, upon switching on of a power supply, initialization of the printer engine is performed (S1). This initialization includes, e.g., initialization of a central processing unit (CPU) as the center of the engine control section 101 and processing of raising the temperature of the fixing device to that of a predetermined standby state. After initializing the printer engine, the engine control section 101 waits for a print request from the printer controller 100 (loop processing in S2).
Upon receiving the print request (/PRNT="LOW"), the engine control section 101 drives the paper conveyor system including the photoconductive drum 1 and initializes the high-voltage devices for charging, developing, and transfer. The engine control section 101 also initializes the scanner motor to a predetermined rotating speed.
When these processing operations are finished, the engine control section 101 starts paper feed from a manual paper feed port as a designated paper feed port (S3). At this time, the registration rollers 11 are kept stationary until the leading end of paper abuts against them. Thereafter, when the paper is detected by the registration sensor and a time required for the leading end of the paper to abut against the registration rollers 11 has elapsed, the engine control section 101 stops the manual paper feed and outputs a vertical sync request signal (/VSREQ) to the printer controller 100 (S4 and S5). Upon receiving a vertical sync signal (/VSYNC) from the printer controller 100, the engine control section 101 starts driving of the registration rollers 11 and activates a count-up timer for paper size measurement (S6 to S8). When no paper is detected by the registration sensor (S9), the count-up timer is stopped (S10). This timer value is defined as T1. The engine control section 101 already has as its data a reference timer value T2 corresponding to each size to be designated by the printer controller 100. When no paper is detected by the registration sensor, the engine control section 101 compares the two values T1 and T2 (S11 to S13). Note, in this comparison, that timer values of .+-..alpha. are added as a margin in consideration of measurement errors and errors in paper length. If the condition of T2-.alpha..ltoreq.T1.ltoreq.T2 +T2+.alpha. is met, the engine control section 101 determines that the paper size is in accord with the designated size. If this condition is not met, the engine control section 101 determines that the paper size is different from the designated size and informs the printer controller 100 of a printer not ready state by using flag information (S13.fwdarw.S21). Once the printer not ready state is set, a print enable state cannot be set unless change designation for the designated paper size from the printer controller 100 is received.
FIG. 4 shows the relationship of T1, T2, and .alpha. in correspondence with paper.
In the above conventional printer, however, even if discord between paper sizes is detected because, for example, paper larger than the designated size is fed, that is, even if no printing data is lost, an error is detected to set the printer in the not ready state, and this disables continuation of printing.
This means that when, for example, the above sequence control is applied to an apparatus, such as a facsimile apparatus, which operates in unattended environments, the above problem disables the subsequent printing although no printing data is lost. For this reason, apparatuses using this sequence control are not easy-to-handle apparatuses for users.
FIG. 5 shows a control sequence of the engine control section 101 when manual paper feed designation is performed in accordance with another conventional technique.
First, the engine control section 101 checks whether a print request (PRNT signal) from the printer controller is received (El). If the request is received, the engine control section 101 starts paper feed from the manual paper feed port (E2). At the same time the engine control section 101 initializes the high-voltage system, the optical system, and the driving system and waits until the leading end of the paper reaches the registration sensor (E3). If the paper has reached the registration sensor, the engine control section 101 outputs a VSREQ signal, as a vertical sync request signal, to the printer controller (E4). Thereafter, upon receiving a VSYNC signal from the printer controller (E5), the engine control section 101 drives the registration rollers that have been kept stopped (E6). At the same time, the engine control section 101 checks whether a paper size is currently designated by the printer controller (E7). If the size is designated, the engine control section 101 sets a timer corresponding to the designated size (E8). If no size is designated, the engine control section 101 sets a timer corresponding to the maximum paper size usable by the printer (E9). At the end of the timer count, the engine control section 101 checks whether a print request for the next page is present (E11). If the print request is present, the engine control section 101 starts the manual paper feed (E2); if not, the engine control section 101 stops the high-voltage, optical, and driving systems to finish the printing.
Even when sheets of paper at the manual paper feed port are used up during the control, the paper size mode already designated is not switched. If a user wishes to change the paper size, he or she externally enters a new paper size.
In this conventional printer, however, if no paper size is designated by an external equipment, the operation is performed by a sequence corresponding to the maximum paper size usable in the printer, and the result is a decrease in throughput. If a paper size is designated, on the other hand, a user must enter another paper size from an external equipment in order to change the paper size, resulting in a cumbersome operation.
FIG. 6 is a block diagram for explaining paper size recognition processing of an image forming apparatus of the type described above.
Referring to FIG. 6, a fixing unit 36 generates heat when a power supply 42 supplies power to a heater 43. A buffer 40 transfers an ON/OFF signal from an MPU 39 to a relay 41, and the voltage from the power supply 42 is supplied to the heater 43 by this ON/OFF signal. The MPU 39 includes a ROM that stores CPU control programs for controlling the laser beam printer, a RAM 60 used to write and read various control data, such as flags for control, in and from it, or the like. The RAM 60 has preset areas E1 to E5 for storing length data L1 to L5 related to usable recording media, such as regular sizes B4, A4, B5, Legal, and Letter.
Buffers 47-l to 47-m transfer the control data from the MPU 39 to individual actuators including a clutch. Buffers 48-l to 48-n transfer detection signals from various sensors (not shown) to the MPU 39. A controller unit 49 controls a printer engine in the laser beam printer. That is, the controller unit 49 controls the laser beam printer through an interface signal line 50 to output an image signal, thereby causing the printer to perform a print operation. A counter 51 counts pulse signals 53 supplied after application of a reset signal 52 and delivers count data 54 to a conveyance distance detector 55.
The image forming apparatus incapable of detecting the size of a recording medium before printing is arranged as described above, so the apparatus must store the lengths of usable recording media, such as the data L1 to L5, and these data undesirably occupy the memory area of the RAM 60. In addition, poor printing or conveyance may be caused when discord is determined in comparison of the medium length with the length data, and this makes it impossible to perform efficient image formation processing.